This invention relates to providing instantaneous hot water to remote faucets in residental or small commercial buildings. Providing instantaneous heated water to remote hot water faucets has proven to be a difficult task when hot water use at the faucet is sporatic. The inconvenience of turning on the water and waiting for hot water to flow from the heater to the remote faucet is agravated in ranch style and two story homes where hot water lines can achieve lengths of 25 meters or more. It is also wasteful of energy and water to run water down the drain while waiting for the hot water to reach the faucet.
Many system approaches and components have been tried with only qualified success. These approaches generally employ one of two basic concepts: (1) Heating the water locally, and (2) circulating hot water from the heater to the remote faucet and back to the heater through a separate return line.
The concept of heating the water in the vicinity of the faucet involves installation of a separate water heater, usually located in the basement close to the remote faucet. These heaters are normally smaller units than the principal building water heater, however still involve all the necessary installation provisions such as an energy source, a gas line for example, and significant plumbing modifications, as shown in U.S. Pat. No. 4,236,548 to Howard. Depending upon the geometry of the installation, the remote heater may still be some distance from the remote faucet, with the result that the delay in receiving heated water is merely reduced. The time reduction will be in direct proportion to the change in the distance from the effective heater to the faucet.
Small undersink heating units such as described in U.S. Pat. No. 1,351,779 to Mather are much closer to the faucet and provide hot water almost immediately. However, these units are generally designed to provide extremely hot water for direct use in making soups or tea and must be mixed with cold water to be of use for typical functions such as hand washing or dish washing. They are often connected to a separate faucet, and constitute a safety hazard due to their extreme high temperature. In addition, they normally have a limited size hot water reservoir that is quickly expended. The undersink units are electrically heated which is costly to operate, and adds the expense of providing an electrical power outlet for the unit.
The systems that use a hot water circulation approach can be broken into two distinct group; pumped circulation, and convective circulation.
Pumped circulation systems such as shown in U.S. Pat. No. 4,142,515 by Skaats, and in U.S. Pat. No. 4,936,289 to Peterson, are effective in providing instantaneous hot water for large commercial buildings, however they have several drawbacks for the average residential or small commercial building. Many new components are added including either timers or thermostats/electronics, a motor, impeller, seals, bearings, wiring, and switches, with their attendant increase of cost and decrease in reliability. They are insensitive to hot water requirements since the pump is controlled by the timer or thermostat and will run on a preset schedule with no regard to hot water needs, thereby wasting the energy to run the pump. Also, heat is lost due to keeping the water line hot at all times, even when no one is in the building, and at night. Electrical power must be supplied through a power outlet installed near the pump. Although the pump motor is small, a humming noise may be transmitted through the pipe to other parts of the building when the pump is running, which may be distracting to some people.
Convective circulation as shown in U.S. Pat. No. 3,097,661 to Lee, and U.S. Pat. No. 3,929,153 to Hasty for example, appears to be a more sophisticated approach in that it uses gravity as the moving force, and has only one moving part, the closure device in a check valve. The initial drawback with a simple convective system is that it requires an upward sloping hot water line to the faucet, and a downward sloping water return line to induce good circulation as discussed by Hasty. In an existing building, the upward sloping line to the faucet is difficult and expensive to achieve.
A more significant problem with a simple convective approach is that with a design that has a circulation flow adequate to keep hot water at the remote faucet, considerable heat is wasted in keeping the pipe hot at all times as discussed by Skaats. In this approach, the return line must be sized large enough to allow a significant flow rate, and the hot water pipe to the remote faucet is kept near heater temperature. Heat loss is proportional to the temperature difference between the pipe and the surrounding environment, so the high temperature of the pipe causes excessive heat losses. Another problem with a simple convection system is that of undesirable heating of the cold water pipe as also discussed by Skaats. Heating of the cold water pipe occurs as a result of the hot water being continuously circulated back to the cold water inlet to the heater and associated pipes. To draw cold water from a cold water faucet in this situation, requires running water to the drain until the warm water is purged which is wasteful of time, water, and heat. If the return line is orificed to reduce the flow rate to minimize these effects, then the convection flow rate will be too low to maintain the pipe hot during periods of infrequent water use. Thus, a simple convective flow circulation system is totally insensitive to hot water needs, and wastes heat most of the time in order to provide heated water to the remote faucet in a timely fashion when it is needed.
It is therefore the principal objective of the present invention to provide a hot water circulation apparatus that when installed in a water system will supply heated water instantaneously to remote hot water faucets in response to user needs. It should also be self regulating to avoid waste of water or energy, and to avoid excessive heating of the cold water system. The apparatus should be reliable, easy to install, economical, and maintenance free.